This invention relates to engines and, more particularly, to engines in which a swash plate is used to convert reciprocal motion of a piston to rotary motion of a drive shaft.
A swash plate engine is an engine in which reciprocal piston motion is converted to rotary shaft motion by means of a swash plate fixedly attached to the shaft at a tilted orientation. Typically, such an engine has several elongate cylinders arranged symmetrically about an elongate drive shaft and the longitudinal axes of the cylinders and the shaft are parallel. In the prior art, each cylinder has a piston and piston rod that move reciprocally and the piston rod has an outer end which extends out from its respective cylinder and connects to a wobble plate which is in slidable contact with the tilted swash plate. When the piston moves longitudinally in the cylinder the piston rod pushes on the wobble plate causing the swash plate to rotate to accommodate the motion of the piston rod. Reaction forces by the swash plate on the piston rod (via the wobble plate) would tend to displace the piston rod away from a central location in the cylinder if the piston rod were not restrained in some way.
Prior art swash plate engines incorporate the wobble plate to control radial and circumferential piston rod displacement in order to maintain a desired predetermined orientation of the rods with respect to their respective cylinders so that the piston rod can transmit force from the piston to the swash plate. The wobble plate is free to move longitudinally of the shaft with the ends of the piston rods but is restrained against rotation about the shaft. The outer end of each piston rod is pivotally attached to the wobble plate. In a swash plate engine the cylinders are usually arranged concentrically about the drive shaft and the pistons reciprocate in a sequential order so that as one piston reaches the top end of its stroke the piston of the diametrically opposed cylinder will be at the bottom of its stroke. Therefore, the wobble plate nutates, without rotation, about the longitudinal axis of the shaft as the pistons move in sequence. As the wobble plate nutates it exerts pressure against the oblique surface of the swash plate causing the swash plate, and the shaft, to rotate. Bearings between the swash plate and wobble plate reduce friction at their interface.
Relevant prior art patents that disclose the use of a wobble plate, or the general equivalent, for converting reciprocal motion to rotary motion include: Lleo et al., U.S. Pat. No. 1,355,484 disclosing a ring piece connected to the piston rods; Davol, U.S. Pat. No 1,656,884 disclosing a "wobbling knuckle"; and Sherman, U.S. Pat. No. 2,475,295 disclosing a wobble plate. All of these prior art patents disclose a means of maintaining piston rod alignment that includes a significant moving mass.
The mass of a wobble plate presents a problem in prior art swash plate engines. Because the wobble plate is pivotally connected to the ends of the piston rods it is therefore a part of the mass that the engine must continuously accelerate, which limits the efficiency of the engine. What is needed, then, is a swash plate engine that maintains piston rod alignment without adding unnecessary moving mass, in order to improve engine efficiency.